The present invention relates to optical instruments and more particularly optical instruments to deflect (steer), modulate, and shape a laser beam using all optical waves.
Older methods to steer, modulate and shape light beams involve movable mirrors and/or polarization rotators and/or acousto-optic elements such as acousto-optic drivers and electro-optic crystals, and lenses. In the prior art, acousto-optic modulators work on the principle of an acoustic (sound) wave being launched in an electro-optic crystal or liquid and inducing a modulation of the refractive index (a refractive index grating) in the crystal. An incident optical beam is steered and/or modulated by scattering light from this refractive index grating in a Raman-Nath diffraction process. The limitations of the acousto-optical beam deflection technique are (i) a source for generating acoustic waves is required, (ii) the acoustic source must be coupled to the electro-optic crystal because it is difficult to adjust the intensity and size of the acoustic source due to inadequacies of the acoustic wave generator whereas a laser beam can be passed through a variable spatial filter such as a variable sized aperture, as well as a variable neutral density filter, (iii) it is very difficult to shape the acoustic wave fronts and hence the refractive index grating planes in the material, and (iv) the acoustic waves launcher and its associated electronics at the launcher-crystal interface can be susceptible to large electromagnetic pulse disturbances or other forms of radiation. In contrast, the all-optical beam modulator as well as deflector and shaper of the present invention have none of these disadvantages.